1. Field of the Invention
Embodiments of the present invention relate to, but are not limited to, electronic device manufacturing, and in particular, to the field of photolithography employing patterned masks.
2. Description of Related Art
In the field of integrated circuit (IC) manufacturing, a process known as photolithography is typically employed in order to form circuitry features onto, for example, a silicon wafer. In the process, an exposure operation is performed whereby selective portions of a photoresist film that is disposed on the wafer surface is exposed to electromagnetic radiation. The type of electromagnetic radiation used will depend upon the sizes of the circuitry features being formed. Typically, the smaller the size of the circuitry features being formed, the shorter the wavelengths of the electromagnetic radiation will be.
The current trend is to build IC with smaller and smaller circuitry features. As the circuitry features become smaller, the wavelengths of the electromagnetic radiation used in the photolithography process is likewise becoming smaller. In fact, electromagnetic radiation at the low end of the spectrum such as deep ultraviolet (DUV) radiation, which is radiation having wavelengths in the range of 125 to 250 nanometers (nm) and even extreme ultraviolet (EUV) radiation, which is radiation having wavelengths around 13.5 nm, are currently being investigated for use in photolithography processes for forming very small circuitry features.
In order to selectively expose only certain portions of the photoresist film to electromagnetic radiation, the radiation is transmitted to the photoresist film using a patterned mask. Depending on the specifics, the patterned mask used may be a transmissive type or a reflective type of patterned mask. For example, when the photolithography process is employing EUV, the patterned mask used in the process will typically be a reflective type of patterned mask.
Reflective types of patterned mask are typically formed by forming a pattern of absorptive material on top of a blank mask (herein “blank”). The blank typically includes a base substrate layer, a reflective multilayer and other layers such as buffer layers. The pattern is formed on the blank by first depositing a layer of radiation absorption material on top of the blank. The layer of absorption material is then patterned using, for example, an electron beam mask pattern generator (herein “electron beam generator”). The electron beam generator is typically controlled by some sort of control or computer device that includes a processor coupled to a memory device containing topography data of the pattern to be formed.
One problem currently faced by IC manufacturers is the problem of mask defects (herein “defects”) that may be present in the patterned masks. These defects include multilayer defects that are embedded within the mask itself. The presence of defects may produce unwanted shadows and/or dispersion of the exposure radiation, which may reduce manufacturing yields. Unfortunately, removing defects that are present in the masks is often extremely difficult, particularly multilayer defects.